This application is a 371 of PCT/GB99/02808, filed on Aug. 25, 1999.
The present invention relates to the use of a menthyl ester as an insect repellent, to compositions containing the menthyl ester and to a method of repelling insects.
Insects have long been known as a nuisance and, for some insect genera, as a health hazard. Mosquitoes, for instance, are a proven vector of diseases, and the genus Aedes in particular is associated with yellow fever, dengue, encephalitis and malaria (Encyclopaedia Britannica). Although the problems may be reduced at source with the use of DDT and other chemical sprays in the breeding areas, fears over the persistence of chlorchemicals combined with increasing mosquito resistance to control chemicals (e.g. insecticides) have led to a reappraisal of the magnitude of the nuisance and the hazard. Physical barriers to the insects are not always possible, e.g. in the open air, where some form of personal repellent is necessary.
It is also a feature of recent times that the more environmentally-aware public tend to question the safety of many chemicals which were formerly taken for granted. One of these is the well-known personal insect repellent N,N-diethyl-m-toluamide (abbreviated as DEET, and commercially available as Delphone (trademark). This was originally seen as the natural successor to the parent molecule, N,N-diethylbenzamide which was found to be strongly insect repellent but also irritating to human skin (McCabe et al., (1954), J. Org Chem. 19, 493-498). Fears over possible allergenicity, disclosed in European Patent Application No. 167266 (Angus Chemical Company), as well as aversion to some of the physical properties of this compound such as oiliness and odour, have led to the search for less hazardous and more aesthetically acceptable methods of repelling insect pests, particularly mosquitoes.
Certain compounds have long been known to posses insect deterrent properties, some of this information coming from what might be termedxe2x80x9cfolk knowledgexe2x80x9d. These materials include widely-known substances such as Citronella, Tolu and Peru Balsams, Eucalyptus oils, Huon Pine and other similar oils [M. Bouvier, International Frag. Co-ord. Oct. 29, 1976]. Other materials known for their deterrent properties include those having camphoraceous odours, such as Camphor itself, Cypress oils, Galbanum etc. [HandR Contact, 36, 1984].
A more scientific approach to the properties of these natural sources has been undertaken by various researchers, such as Lemberkovics et al. [Acta Pharmaceutica Hungarica, 57, (1987) 133-142], Nahrstedt [Planta med. 42(4), 313-32 (1981)], and Popescu [Chim. Anal. (Bucharest), 2(1), 59-61 (1972)] who investigated the effects of Walnut Leaf oil. Kumbu and DiPhanzu [Plant Med. Phytother. 16(1), 23-6 (1975)] investigated the deterrent effect of a range of Eucalypts against a selection of insect pests.
The popularly-used DEET has also been studied in comparison, and in conjunction, with a range of ingredients by various researchers. Nishimura et al. [Kagaku to Seibbutsu, 27(8), 4886-6 (1989)] investigated the possible synergy of Eucalyptus citriodora and menthanediols with DEET. Solvents such as diethyl phthalate, dimethyl phthalate and dibutyl phthalate are also well known, and these provide the basis for commercial repellents which do not contain DEET, and are also cited in Kirk-Othmer Encyclopedia of Chemical Technology [3rd Edn., Vol. 13, 476ff]. Canadian patent 1 230 826 (1988) uses a combination of Citronelia or Lavender oils, 2-ethylhexanediol and dimethyl phthalate.
Repellent chemicals may be classified into two main groups: general deterrents and species-specific deterrents. Substances known to deter one species have been known to serve as an attractant to another. An example of this is the use of a mixture of citronellol and eugenol against clothes moths and Anthrenus beetles, described in German patent application DE 3 901 341A [published 1990, Detia Freyberg GmbH]. The latter ingredient, Eugenol, is considered to be a general insect attractant [Kirk Othmer Encyclopedia of Chemical Technology, cited above]. DEET, however, is considered to be a general, or broad-spectrum, insect repellent. Materials potentially useful as insect repellents are frequently tested against mosquitoes, in particular against the genus Aedes. These materials may also act as general insect repellents.
PCT Application WO 96/08147 discloses the use of a number of different compounds as insect repellents and also a method by which the repellency of compounds to insects can be reliably tested. UK Patent GB 1 567 496 discloses a number of terpene esters of 2-pyrrolidone-5-carboxylic acid which are useful in anti-inflammatory topical compositions. These esters are effective as long lasting physiological coolants and their efficacy is believed to be due to enzymatic hydrolysis on skin that ensures a low level of hydrolysed terpene alcohol (e.g. menthol), which provides a coolant effect, and pyrrolidone carboxylic acid, a natural moisturising factor which conditions the skin.
It has now been surprisingly found that the menthyl ester of 2-pyrrolidone-5-carboxylic acid is an effective insect repellent under conditions in which the above-mentioned hydrolysis is not believed to occur. It has also been shown that the ester is a more effective insect repellent than its hydrolysis product, menthol, and the superior repellency is maintained for at least I hour after application to a substrate.
Consequently, the invention comprises the use of menthyl 2-pyrrolidone-5-carboxylate as an insect repellent.
Menthyl 2-pyrrolidone-5-carboxylate is commercially available under the Trade Mark QUESTICE but it has not heretofore been recognised as an insect repellent.
In another aspect, the invention provides a method of repelling insects from an object or an airspace, comprising application to the object or into the airspace, of an effective amount of menthyl 2-pyrrolidone-5-carboxylate. Typically the object is a human body.
The menthyl 2-pyrrolidone-5-carboxylate used as an insect repellent in accordance with the invention can be used in the form of a composition which contains components other than menthyl 2-pyrrolidone-5-carboxylate. In one embodiment, the composition is a perfumed composition.
Preferably, the menthyl 2-pyrrolidone-5-carboxylate composition defined above is used to repel biting insects, such as mosquitoes, particularly members of the genus Aedes.
The composition used in the invention, whether perfumed or not, preferably contains at least 0.05% by weight, more preferably at least 0.5% by weight, and most preferably at least 2.0% by weight of menthyl 2-pyrrolidone-5-carboxylate. Compositions containing not more than 10% by weight of menthyl 2-pyrrolidone-5-carboxylate have been shown to be effective insect repellent compositions.
Compositions used in accordance with the invention preferably constitute, or comprise, personal products or cosmetics for use on the skin and/or hair. Examples of such products include fine fragrances, colognes, skin creams, skin lotions, deodorants, talcs, bath oils, soaps, shampoos, hair conditioners and styling agents.
Alternatively, compositions used in accordance with the invention may constitute, or be comprised in, household products such as: air fresheners (includingxe2x80x9cheatedxe2x80x9d air fresheners in which insect repellent substances are released upon heating e.g. electrically, or by burning [e.g. joss-sticks, candles]), hard surface cleaners or laundry products (e.g. laundry detergent-containing compositions and conditioners).
Preferably the cosmetics, personal products and household products defined above comprise between 0.1% and 10% of a composition used in accordance with the invention.
The compositions used in the invention may comprise additional materials to produce desired products such as pleasing perfumes with useful repellent activity. Other materials which may be present in the compositions (at concentrations from 0 to 99.95% by weight) include fragrances, solvents, diluents and fixatives known in the art, such as: Aldehyde C11 (Undecylenic Aldehyde); Aldehyde iso C11 (GIV); Allspice oil; Allyl cyclohexyl propionate; Amyl salicylate; Amylcinnamic aldehyde; Anethole; Anisic alcohol; Anisic aldehyde; Applinal (Q); Bay oil; Benzyl acetate; Benzyl benzoate; Benzyl cinnamate; Benzyl propionate; Benzyl salicylate; Bourgeonal (Q); Brahmanol; Camphor powder synthetic; Cedarwood Virginion; Cedrenol; Cedryl acetate; Celestolide (IFF); Cineole; Cinnamic alcohol; cinnamic aldehyde; Cinnamon Leaf Oil; Cinnamyl acetate; cis-3-Hexenol; Citral; Citronella oil; Citronellal; Citronellol; Citronellyl acetate; Citronellyl oxyacetaidehyde; Clove oil; Coriander oil; Coumarin; Cuinic aldehyde; Cyclamen aldehyde; Decanal; 9-Decenol; Dibenzyl ether; Dibutyl phthalate; Diethyl Phthalate; Dihydromyrcenol; Dimethyl anthranilate; Dimethyl phthalate; Dimycretol (IFF); diphenylmethane; Diphenyl oxide; Dimethyl benzyl carbinyl acetate; Dodecanol; Dodecanal; Elemi oil; Ethyl methyl phenyl glycidate; Ethyl cinnamate; Ethyl safranate (Q); ethyl vanillin; Eugenol; Evergreen oils (Pine oils etc.); gamma-Nonalactone; gamma-undecalactone; Cardamide (Q); Geraniol; Geranium bourbon; Geranyl acetate; Geranyl formate; Gum Benzoin; Heliotropin; Hercolyn D (HER); Hexyl benzoate; Hexylcinnamic aldehyde; Hydratropic aldehyde dimethyl acetal; Hydroxycitronellal; Hydroxycitronellal dimethyl acetal; Indole; iso Bornyl acetate; Isolongifolanone; Isopropyl myristate; Iso-cyclocitral (GIV, IFF); Jasmacyclene; Jasmin oil; Lavandin Abrialis; Lavender oil; Lilial (GIV); Linalol; Linalyl acetate; Maceal (0); Menthol Laevo; Methyl anthranilate; Methyl cedryl ketone; Methyl dihydrojasmonate; Methyl ionone; Methyl ionone alpha iso; Methyl myristate; Methyl naphthyl ketone; Methyl salicylate; Moss treemoss; Musk ketone; Neocaspirene (Q); Nerol; Nerolin Bromelia; Neryl acetate; Nonanal; Oakmoss absolute; Octanol Olibanum resinoid; para-Cresyl phenylacetate; para-Methoxyacetophenone; Patchouli oil; Peppermint oil; Petitgrain oil; 2-Phenoxyethanol; Phenoxyethyl iso butyrate; Phenylethylacetate; Phenyethyl alcohol; Phenylethyl butyrate; Phenylethyl phenylacetate; Pimento oil; Pinene, alpha; Para-tert. butyl-cyclohexyl acetate; Resinoid Benzoin Siam; Rose oil; Rosemary oil; Sandalwood oil; terpineol; Tetrahydrolinalol; Tetrahydromuguol (IFF); Thyme Red; Undecanal; Vanillin; Verbena oil; Vetyvert Bourbon; Yara and Ylang ylang.
Compounds are obtainable from the suppliers as indicated below: for those compounds labelledxe2x80x9c(Q)xe2x80x9dxe2x80x94Quest International,xe2x80x9c(IFF)xe2x80x9dxe2x80x94International Flavours and Fragrances, Inc., xe2x80x9c(GIV)xe2x80x9dxe2x80x94Givaudan,xe2x80x9c(HER)xe2x80x9dxe2x80x94Hercules B.V.
Other active and non-active materials may be present, such as:
acidic mucopolysaccharides and their salts, Aesculus hipocastanum, aloe barbadenisis Mil (Aloe Vera Linne), xcex1-hydroxycarboxylic acids, xcex1-ketocarboxylic acids, amide derivatives, amino acids, amphiphilic cyclodextrin derivatives, xcex2-sitosterol, carboxy vinyl polymer water soluble salts, carboxymethyl cellulose, carrageenan, chitin, chitosan, cholesterol, cholesterol fatty acid ester, collagen, dicarboxylic acid monostearyl esters, di-fatty acid glycerol esters, digalactosyl diglyceride, ersterol, ethanol, extract of Swertia japonica Makino, fatty acids, fatty acid citrate esters, fatty alcohols, ginseng extract, glucose esters of higher fatty acids, guar gum, gum arabic, Hamamelidaceae (Hamamelis Virginiana Witch hazel), hyaluronic acid, hydrochyloesterol, hydroxybenzoic acids, isomaltose, isopropyl alcohol, lactose, lanosterol, lipids extracted from the biomass of microorganisms, yeasts, moulds and bacteria, liposomes, locust bean gum, low molecular acidic mucopolysaccharides and their salts, low molecular weight humectant components, maltose, mineral oils, mineral powders, monocisalkenoic acid, mucopolysaccharides, mycosterol, N-acyl lysines, N-isostearyl lysine, N-lauroyl lysine, N-myristyl lysine, N-palmitoyl lysine, N-stearoyl lysine, natrium type bentonite, natural or synthetic aminoacid with protein or peptide bonds, NMF ingredients, nonvolatile silicones, oil agents, oil matter, oligosaccharides, organic acids, pantothenic acid and its derivatives, petroleum jelly, phosphatidyl ethanolamine, phosphatidylcholine, phospholipids, polysaccharides, polyvinyl alcohol, polypeptides, proteins, raffinose, saponins, sodium hyaluronate, sources of linoleic acid, sterols, sterol esters, stigmasterol, sucrose, sugar esters of higher fatty acids, sulphatide, sunscreens, surfactants, talc, thymosterol, tocopherol, mono-, di- or tri-glycerides, vitamins and analogues, vitamin E and/or its ester compounds, volatile silicone fluids, water-soluble moisture-retaining agents, water-soluble polymers and waxes.
Menthyl 2-pyrrolidone-5-carboxylate can be used as the sole insect repellent in a composition or may be used in combination with other compounds which are effective insect repellents.
A further aspect of the invention comprises a mixture of menthyl 2-pyrrolidone-5-carboxylate with a known insect repellent. Known insect repellents which are suitable for use in a mixture with menthyl 2-pyrrolidone-5-carboxylate include N,N-diethyl-m-toluamide (DEET); N,N-diethylbenzamide; citronella; Tolu balsam; Peru balsam; Eucalyptus oil; Huon pine oil; camphor; cypress oil; galbanum; diethyl phthalate; dimethyl phthalate; dibutyl phthalate; 1,2,3a,4,5,5a,6,7,8,9,9a,9b-dodecahydro-3a,6,6,9a-tetra-methyinaphtho[2,1-b] furan; 4-(tricyclo [5.2.1 .02,6]decylidene-8) butanal; 1-ethoxy-1(2xe2x80x2-phenylethoxy)ethane; acetyl cedrene and propylidene phthalide.
A composition according to the invention also comprises a mixture of menthyl 2-pyrrolidone-5-carboxylate and a second compound, said second compound having a repellency of at least 20% as determined by the insect repellency test defined in Example 1. Preferably, the second compound has a repellency of at least 40%, more preferably at least 50%, according to said test.
A further composition according to the invention comprises a mixture of menthyl 2-pyrrolidone-5-carboxylate and a second compound, said second compound being present in an amount which is sufficient to ensure that said second compound contributes to said composition an insect repellent effect equivalent to a repellency of at least 10% as. determined by the insect repellency test defined in Example 1. Preferably, the second compound is present in said composition in an amount which is sufficient to ensure that said second compound contributes an insect repellent effect equivalent to a repellency of at least 20% as determined by said insect repellency test. More preferably, the insect repellent effect contributed by the second compound is equivalent to a repellency of at least 30%.